92 F. W. GAMBLK, M.8C., AND J. H. ASHWORTH, B.SC. 



The tail, which is devoid of setse and gills, is marked by a large 

 number of secondary annuli, crowded together at first, but arranged in 

 distinct somites of about five each, towards the hinder end. The 

 caudal region varies much in length ; some specimens have about 

 thirty somites, but the number is not constant possibly owing to the 

 tendency of the worm to throw off the last few segments when irritated. 



There is no change in the internal organs to mark the somite which 

 bears the first gill, but the transition from the branchial to the caudal 

 region is accompanied by the loss of parapodia, oblique muscles, and 

 branchial vessels. 



External Apertures. — The mouth (PI. IX., Fig. 19, C. MO.), when 

 the proboscis is withdrawn, is a slightly crescentic transverse slit, 

 bordered by papillse and somewhat overhung by an upper lip. The 

 anus, which is terminal, is often proti-uded, and the thin vascular 

 swollen lips of the aperture project behind the last caudal segment. 



The cpeuiug of the " nuchal organ" is a fairly wide slit on the upper 

 and hinder border of the prostomium (PL. IX., Fig. 19, a and b, NV.). 

 Through this aperture, sea water (or a mixture of sea water and the 

 secretion of the surrounding glandular cells) is pi-obably introduced. 



The openings of the otocysts are difficult to see. They lie behind 

 the prostomium on each side of the anterior end in the position marked 

 OT. (PI. IX., Fig. 19, a and b). Each is placed at the point of inter- 

 section of the first transverse groove following the prostomium, with 

 the oblicpie " metastomial " groove which marks the position of the 

 nerve commissure. 



The nephridial openings (Fig. 1, NO), six in number on each side, 

 though not so distinct as in some species {e.g. A Claparedii), are not 

 difficult to find. The first is placed behind at the upper edge of the 

 fourth neuropodium, and the other five in corresponding positions on 

 the succeeding somites. They are minute slightly oblique slits, some- 

 times exhibiting tumid lips. 



Skin. — The skin is subdivided into raised polygonal areas separated 

 by corresponding shallow grooves, and is noteworthy in being devoid of 

 special glands. Wiren (1887) has shown that the grooves are composed 

 of columnar cells containing pigment granules, the raised areas being 

 made up partly of larger cells containing still greater quantities of 

 pigment granules and partly of clavate mucus-forming cells, which 

 produce the slimy covering of the animal with which the burrow is 

 lined. 



